They are the most widely used method of regulating the mixture intake flow in 2-stroke engines. Geometry and materials, as well as the position of these components, are fundamental aspects for the performance and reliability of kart engines
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WHAT IS IT?
HOW DOES IT WORK?
IN PRACTICE
2T engines do not have intake and exhaust valves, unlike 4T. Instead, they use different systems that regulate the mixture flow from the carburettor to the engine. One solution is called “reed valve intake”, another “piston port”, and a third “rotating valve”. Starting from the latter, one could say that the system certainly simplifies the structure of the engine, but at the same time does not offer the performance of the first two mechanisms. Nowadays, with racing engines mainly designed for elasticity of use, rotating valves have been put to one side a little in favour of the other twosystems. The “pistonport” is compulsory in many junior class regulations. However, the most widely used is now the “reedvalve” system, which has the ability to adapt to the various engine speeds more effectively than the rotating valve.
Since the reed valve works with a frequency of opening and closing that, in theory, is equal to the number of engine revolutions, it's clear that this component must be extremely light, in order to minimise inertia due to weight and follow engine revs more effectively; durable, so that it can flex quickly countless times without breaking; elastic, so that it quickly returns to the default position (closed) after each engine revolution. The materials that are best suited to these mechanical features are composites such as glass fibre and, better still, carbon fibre. Consider that the modulus of elasticity, i.e. the value that indicates the ability of a material to return to its original shape once elastically deformed, of carbon fibre is up to 3 times that of steel, while specific weight is less than a quarter and specific resistance exceeds 10 times that of steel.
ON 2-STROKE ENGINES, THE INTAKE CAN BE REGULATED BY PISTON PORT, REED VALVE OR ROTATING VALVE SYSTEMS. THE LATTER NOW HAVING ALMOST DISAPPEARED
The components of reed valve pack
WHAT IS IT?
HOW DOES IT WORK?
IN PRACTICE
REED VALVE DISTRIBUTION
THE EFFECT OF THE EXHAUST RESONANCE ON REED VALVE OPENING
The waves of pressure generated by the exhaust ports reach the reed valve pack through the combustion.
In this way, even before the depression in the carter pump occurs, the depression waves reach the reed valves and lift themRead more
RESONANCE OF THE REED VALVE
One of the limits of reed valves is that they sometimes “resonate” at high engine speeds, flexing in the opposite direction to that of the opening or closing, and thereby reducing the open section or even the partial closure of the passage.Read more
Reed valves may have different forms, but in general in kart engines they are made in pairs consisting of two petals shaped like an isosceles trapezium with rounded corners (to avoid breakage and turbulence affecting the mixture flow). The reed valves can then have holes (reduced and well finished to limit the weakening of the structure) at the base that attaches to the reed valve pack, in areas in which mixture does not flow:
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Utente che approccia per la prima volta il mondo del karting. Non ha mai avuto un kart proprio oppure lo possiede da pochi mesi. Gli mancano tutte le conoscenze di base ed elementari di questo sport e necessita di informazioni che gli permettano di orientarsi. Cerca risposte a domande come: come fare la miscela? Quali strumenti mi servono per gestire il kart? Quali sono le differenze tra la pressione di gonfiaggio delle gomme di un'auto e quelle di un kart? E come trasportare il kart in pista?
Praticante
Utente che pratica il karting da più tempo, gestendo personalmente il proprio mezzo. Conosce le nozioni di base di questo sport, ma desidera rimanere aggiornato sulle novità del settore e ricevere consigli per migliorare le proprie capacità di meccanico e pilota. Cerca risposte a domande del tipo: come installare sistemi di raccolta dati e leggere le informazioni base? Come gestire al meglio le pressioni delle gomme? Come affinare il rapporto del kart per migliorare le prestazioni? Il praticante potrebbe rimanere tale per tutta la vita, preferendo non affrontare questioni tecniche troppo complesse, ma continuando a migliorarsi e divertirsi nel mondo del karting.
Esperto
Si tratta di un utente praticante che non si accontenta delle conoscenze base di questo sport, ma vuole approfondire fino ai massimi livelli ogni singolo aspetto legato alla guida e alla tecnica. L’approccio è pressoché professionale. La discriminante è chiara: il praticante si ferma quando le attività relative al kart diventano complesse, come il cambio di un pistone o della candela, senza però cimentarsi in operazioni più avanzate come la lappatura della canna. L’esperto, invece, non si spaventa di affrontare questioni a complessità elevata, come per esempio equilibrare autonomamente l’albero motore o regolare l’anticipo.